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 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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package com.nulldev.util.graphics.renderIt.ginterfaces.marlin.impl;

import java.lang.ref.Reference;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * This ReentrantContextProvider implementation uses one ConcurrentLinkedQueue
 * to store all ReentrantContext instances (thread and its child contexts)
 *
 * Note: this implementation keeps less contexts in memory depending on the
 * concurrent active threads in contrary to a ThreadLocal provider. However, it
 * is slower in highly concurrent workloads.
 *
 * @param <K> ReentrantContext subclass
 */
public abstract class ReentrantContextProviderCLQ<K extends ReentrantContext> extends ReentrantContextProvider<K> {
	// ReentrantContext queue to store all contexts
	private final ConcurrentLinkedQueue<Reference<K>> ctxQueue = new ConcurrentLinkedQueue<Reference<K>>();

	/**
	 * Create a new ReentrantContext provider using the given reference type among
	 * hard, soft or weak based using a ConcurrentLinkedQueue storage
	 *
	 * @param refType reference type
	 */
	public ReentrantContextProviderCLQ(final int refType) {
		super(refType);
	}

	/**
	 * Give a ReentrantContext instance for the current thread
	 *
	 * @return ReentrantContext instance
	 */
	@Override
	public final K acquire() {
		K ctx = null;
		// Drain queue if all referent are null:
		Reference<K> ref;
		while ((ctx == null) && ((ref = ctxQueue.poll()) != null)) {
			ctx = ref.get();
		}
		if (ctx == null) {
			// create a new ReentrantContext if none is available
			ctx = newContext();
			ctx.usage = USAGE_CLQ;
		}
		return ctx;
	}

	/**
	 * Restore the given ReentrantContext instance for reuse
	 *
	 * @param ctx ReentrantContext instance
	 */
	@Override
	public final void release(final K ctx) {
		if (ctx.usage == USAGE_CLQ) {
			ctxQueue.offer(getOrCreateReference(ctx));
		}
	}
}
